Numerous applications are known in which additive products must be injected into a liquid, for example, in water treatment installations or facilities in which chlorine is injected to render source water potable.
Due to the presence of various salts or compounds dissolved in the water, or the liquid, the injection of chlorine, or other additives, causes chemical reactions which produce insoluble or only slightly soluble salts which precipitate at least partially from the liquid, as in the cited example, calcium may precipitate from treated water.
These insoluble salts often precipitate onto the additive product injection nozzle, or in regions adjacent thereto, and accumulate to form undesirable deposits or concretions capable of obstructing the injection nozzle, or even the conduit through which the liquid flows. Certain sensitive parts of such installations must therefore be dismantled in order to eliminate such deposits at regular intervals, by suitable physico-chemical methods.
Moreover, devices have been proposed for adding chlorine to water in a batch process, by suction produced by the evacuation of a treated water holding tank as water is drawn therefrom. Such a device is described in U.S. Pat. No. 2,418,628. Although in such known devices the problem of accumulation of precipitated salts on the tube through which chlorine is added is not normally posed, such devices are wholly unsuitable for continuous operation as is required of water treatment facilities, as the operation of the chlorine injection circuit is entirely dependent on pressure fluctuations only existing in a batch process installation.